Hydrophilic coatings and films have been described in several U.S. patents and their foreign counterparts. U.S. Pat. No. 4,467,073 describes the reaction of polyisocyanates in the presence of poly N-vinyl lactams and poly N,N-dimethylacrylamide. The stability of these compositions is limited due to the presence of highly reactive isocyanate groups. Such compounds are handled as two part systems, wherein each component is contained in an aprotic organic solvent. The components are combined whereupon crosslinking is effected, in essence, spontaneously. These systems are replete with environmental and toxicity concerns due to the presence of isocyanates and the exhausting of volatile organic solvents to the atmosphere. Environmental conditions when such polyisocyanates/poly-N-vinyl lactams or poly-N,N-dimethylacrylamide are used must be carefully controlled to reduce humidity, eliminate fire hazards and collect or incinerate any toxic vapors. Another anti-fog polymeric composition contains a preformed polyurethane in conjunction with a poly N-vinyl lactam. An example of this is disclosed in U.S. Pat. No. 4,642,267 (Creasy, et. al.). issued on Feb. 10, 1987.
Hydrophilic compositions have also been prepared, containing polyvinylpyrollidone (PVP) with polyurethanes and polyvinylbutyrals. These compositions may be applied from stable solutions that contain alcohol or water. Unfortunately these compositions are relatively non-permanent, reacting with or dissolving in solvents or otherwise becoming softened, such as in the presence of heat. Thus, the hydrophilic properties of the composition may be compromised. Also, if external crosslinking agents are added, these may reduce the hydrophilic properties of the composition or introduce instability.
Anti-fog coatings consisting of polyvinyl alcohol which has been crosslinked with a combination of zirconium nitrate and formaldehyde are disclosed in U.S. Pat. Nos. 4,064,308 and 4,127,682. U.S. Pat. No. 3,700,487 discloses polyvinyl alcohol antifogs crosslinked with an acid and an organotitanate.
One object of the present invention is therefore to facilitate the use of water soluble ingredients in anti-fog coatings.
Another object of the present invention is to obviate the need for organic solvents, and thus avoid the toxic effects which accompany these compounds.
Another object of the present invention is to provide an anti-fog composition that can be used in the form of a film in combination with an adhesive backing to impart the anti-fog properties to various optical products.
Another object of the present invention is to provide an anti-fog composition which can be coated onto a substrate in solution form, dried and cured to render the substrate essentially fog resistant or "non-fogging".
Another object of the present invention is to provide an anti-fogging composition which maintains its anti-fogging properties in humid surroundings even after condensation forms.
Another object of the present invention is to provide a coating composition which is scratch-resistant.
Another object of the present invention is to provide a composition which is hydrophillic and which can be used to reduce water droplet formation on the coated substrate.
Another object of the present invention is to provide water-insoluble coatings with reduced friction properties when wet.
These and other objects will be apparent to those of ordinary skill from the teachings herein.